1. Field of the Invention
This invention relates to brazing of metal parts and, in particular, to a homogeneous, ductile nickel-palladium based brazing material useful in brazing iron, cobalt and nickel based alloys.
2. Description of the Prior Art
Brazing is a process for joining metal parts, often of dissimilar composition, to each other. Typically, a filler metal that has a melting point lower than that of the metal parts to be joined together is interposed between the metal parts to form an assembly. The assembly is then heated to a temperature sufficient to melt the filler metal. Upon cooling, a strong, corrosion resistant, leak-tight joint is formed.
Nickel and cobalt based alloys are conventionally joined by means of hydrogen, inert gas or vacuum brazing techniques. Such methods are employed to maintain low levels of contamination in the joint area.
Precious metal base filler metals are used for the brazing of iron, nickel and cobalt base materials where resistance to corrosion and oxidation is desired. These filler metals are not suitable for joining base metals which have a high heat treatment temperature compared to the filler metal.
A variety of iron, nickel and cobalt based metals can be joined using Ni-Pd-Cr-B filler metals. These alloys cannot be made into foil form by conventional methods due to their inherrent brittle nature. Consequently, where a pore-free joint is required precious metal based filler metals which are available in foil forms are used. These precious filler metals contain a substantial amount of gold and are, therefore, relatively expensive.
Some of the filler metals of Ni-Cr-Pd-B family can be used for diffusion bonding in which the boron diffuses into the base metal. The joint region therefore becomes depleted of boron during the joining process and remelts at a higher temperature. Base metals which have a relatively higher heat treatment temperature can thus be heat treated.
Ductile glassy metal alloys have been disclosed in U.S. Pat. No. 3,856,513, issued Dec. 24, 1974 to H. S. Chen et al. These alloys include compositions having the formula M.sub.a Y.sub.b Z.sub.c, where M is a metal selected from the group consisting of iron, nickel, cobalt, vanadium and chromium, Y is an element selected from the group consisting of phosphorus, boron and carbon, and Z is an element selected from the group consisting of aluminum, silicon, tin, germanium, indium, antimony and beryllium, "a" ranges from about 60 to 90 atom percent, "b" ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to 15 atom percent. Also disclosed are glassy wires having the formula T.sub.i X.sub.j, where T is at least one transition metal and X is an element selected from the group consisting of phosphorus, boron, carbon, aluminum, silicon, tin, germanium, indium, beryllium and antimony, "i" ranges from about 70 to 87 atom percent and "j" ranges from about 13 to 30 atom percent. Such materials are conveniently prepared by rapid quenching from the melt using processing techniques that are now well-known in the art. No brazing compositions are disclosed therein, however.
There remains a need in the art for a homogeneous nickel-palladium based brazing material that is available in ductile foil form.